Method of and apparatus for pumping gas under cryogenic conditions

ABSTRACT

In pumping a gas under cryogenic conditions, condensation surfaces disposed within a receiver containing the gas to be pumped are cooled to a predetermined temperature while the surfaces are thermally insulated from any heat within the receiver. During initial cooling the gas is not permitted to flow over the condensation surfaces. When the predetermined temperature is reached, the gas within the receiver, which is under vacuum conditions, is circulated over the condensation surfaces. The amount of gas flowing over the condensation surfaces is regulated in accordance with the temperature, vacuum and other conditions within the receiver.

States Patent [111 3,535,307

[72] ln nt Jurgen Hengevoss; [56] References Cited Hermann WOSSMI', bothof Balzers, UNITED STATES PATENTS I 21 l A I No kgggg g 3,256,706 6/1966Hansen 62/555 3,262,279 7/1966 Moore 62 555 221 Filed Aug. 18, 19693,472,039 10/1969 Hart 62/55.5 [451 3 485 054 P/l969 H 62 55 5 [73]Assignee Balaers Patent-und Beteiligungsogan l AktiengesellschaitPrimary Examiner-William J. Wye Balzers, Liechtenstein Attorney-McGlewand Toren [32] Priority Aug. 20, 1968 [33] Switzerland h 31 [2,6514ABSTRACT: In pumping a gas under cryogenic conditions, condensationsurfaces disposed within a receiver containing the gas to be pumped arecooled to a predetermined temperature while the surfaces are thermallyinsulated from any heat within the receiver. During initial cooling thegas is not permitted to flow over the condensation surfaces. When the[54] f gg g APP;RATU: g PUMPING predetermined temperature is reached,the gas within the 13 g D 5 D [C CO m IONS receiver, which is undervacuum conditions, is circulated over rawmg the condensation surfaces.The amount of gas flowing over the [52] U.S.Cl 62/55.5 condensationsurfaces is regulated in accordance with the [51] Int. Cl 801d 5/00temperature, vacuum and other conditions within the [50] Field of Search62/555 receiver.

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JAIVENTORJ JURGEN IIENE V035 MAN ms: IVER BY %w i 14 A TTORNEYS' METHODOF AND APPARATUS FOR PUMPING GAS UNDER CRYOGENIC CONDITIONS SUMMARY OFTHE INVENTION The present invention is directed cryogenic a method ofand apparatus for pumping gases under cryogenic conditions wherein thegas being pumped flows over deep-cooled condensation surfaces, and, moreparticularly, it is concerned with the enclosure for the condensationsurfaces within the receiver and with the means for admitting gas forpassage over the condensation surfaces.

In the past, it has been known to use a refrigerator to establish thecryogenic pumping conditions for the starting operation and then tomaintain these conditions at the operating temperature during pumping.The output of the refrigerator is established so that the required lowtemperature cooling is possible in a sufficiently short time. Experiencehas shown that the refrigeration output required to establish the lowtemperature conditions is much greater then is required for thecontinuous pumping operation at pressures below mm. Hg for maintainingthe operating temperature. During normal operating conditions, the heatdirected to the condensation surfaces is predominantly by heat radiationwhereas the heat of condensation liberated by the condensation of thegases being pumped is not of any decisive importance. In bringing theoperating temperature to the desired level under cryogenic operatingconditions, the refrigeration output has to be rated in accordance withthe desired short cooling period, as a result, if the working speeddemanded for a modern industrial pumping station is to be attained, theinitial refrigeration output is required to be several times higher thanthat necessary for actual pumping operation. In cryogenic pumpingoperations conducted by the supply of liquefied gases from a storagetank, there is no problem in obtaining the greater refrigeration outputrequired for the initial cooling phase since it can be supplied by acorrespondingly larger refrigerant supply from the storage tank.

Therefore, it is the primary object of the present invention to improvethe economic efficiency of a cryogenic pumping operation which employsrefrigeration apparatus.

In the prior art where the given output of the refrigerator was employedfor cooling to the desired operating temperature, a radiation protectionwas employed around the condensation surfaces. Such radiation protectionusually consisted of an arrangement of sheetlike members shieldingagainst heat radiation. However, while these sheets permitted the gasbeing pumped to pass over the condensation surface, they constituted aflow obstacle which caused a disadvantageous reduction in the pumpingrate. Accordingly, the present invention is directed to overcoming thisdisadvantageous construction of the prior art.

In accordance with the present invention, in the method of pumping a gasunder cryogenic conditions and employing a refrigerator to obtain thedesired low temperature conditions the novel characteristic involves thethermal insulation of the condensation surfaces from the heat within thereceiver while the surfaces are being cooled to a predeterminedtemperature.

In carrying out the cryogenic pumping operation under high vacuumconditions the surfaces for reducing the gas to the necessary lowtemperatures are disposed within a space containing the gases to bepumped and an adjustably movable device, operable from the exterior ofthe enclosed space, is arranged to admit the flow of gas over thecryogenically cooled surfaces, and the movable device is arranged toprovide a thermal shield for the surfaces while the operatingtemperature is being established. In a known high vacuum cryogenicpumping system, in which the cryogenically cooled surfaces over whichthe gases pass are arranged in a space communicating with the space tobe evacuated, an enclosure device has been used for temporarilyseparating the cooled surfaces from the space to be evacuated. Thisprior device overcame the problem of previous cryogenic pumping systemswherein the water vapor which precipitated on the condensation surfaceshad to be retained until the process being carried out under a vacuumwas completed. This system was not only time consuming and required aconsiderable amount of refrigerant, but it also posed the danger that asudden rise in the temperature within the receiver, which could easilyoccur in the course of such a process, could lead to the release of thewater vapor from the condensation surfaces and result in an undesiredincrease in pressure. By employing the above mentioned enclosure for thecondensation surfaces, it was possible to seal the surfaces from thespace containing the gas to be evacuated and to thaw the water condensedthereon discharging it through a separate pumping line withoutinterfering with the vacuum within the space containing the gas andotherwise interrupting the process. Such operation required that theclosure device was designed to afford a high vacuum seal between thespace containing'the condensation surfaces and the space containing thegases to be pumped. The arrangement which served only to thaw thecondensate during operation is not an element of the present invention.

To attain the objectives of the present invention, as set forth above,the closure device for the cryogenically cooled condensation surfaces ofthe prior art is not sufficient. Under the present invention, it isnecessary during the initial cooling phase to provide a temporarythermal separation between the condensation surfaces and the gas to bepumped. The thermal separation can be effected by providing a thermalshield to enclose the condensation surfaces. Such a thermal shield canbe provided by cooling the surfaces of the shield or by the applicationof a thermal insulating material. A simple covering about thecondensation surfaces, as disclosed in the prior art, is not sufficientbecause the surface of the covering facing toward the condensationsurfaces acts as a heat radiation source of the same intensity as thereceiver, which forms the space containing the gas without the covering,and the condensation surfaces would be exposed to the same temperatures.On the other hand, as compared to the prior art arrangement, it is notnecessary, in accordance with the present invention, to provide agas-proof seal between the space containing the gas and the spacecontaining the condensation surfaces.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the inventionits operating advantages and specific objects attained by its use,reference should be had to the accompanying drawings and descriptivematter in which there are illustrated and described preferredembodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. I is a somewhat schematic vertical sectional view of an apparatusconstructed in accordance with the present invention;

FIGS. 2a and 2b show another arrangement of apparatus in accordance withthe present invention; and

FIGS. 31: and 3b show still another embodiment of apparatus inaccordance with the present invention for pumping gas under cryogenicconditions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. I a receiver 2encloses a chamber 1 which is to be evacuated in effecting the cryogenicpumping operation. Condensation surfaces which are deep-cooled duringthe cryogenic pumping operations are formed with the chamber 1 by meansof a cooling coil 4 through which a refrigerant is passed. Therefrigerant is circulated in a closed cycle flowing into the coolingcoil 4 through and inlet line 5 and passing out through an outlet line 6for flow through a refrigerator 7. In

accordance with the invention, the condensation surfaces provided by thecoil 4 are enclosed during the period in which the surfaces are broughtto a predetermined low temperature. The closure for the condensationsurfaces is provided by a vertically movable hood member 8 which coversthe sides and upper surface of the coil protecting it from any heatsupply within the chamber ll of the receiver 2. A column 9 extends intothe receiver 2 through its base and is secured to the hood member. Avacuum-proof seal is provided by a packing member MB for the openingthrough which the column 9 enters the receiver. Exteriorly of thereceiver, the column 9 is connected to a threaded spindle Ill and bymeans of gear wheels 12 mounted on the spindle and a servomotor I3, thecolumn 9 and the hood 8 can be lifted or lowered within the receiver. Asindicated in dot-dash lines in F [G I, the hood 3 can be lifted from theposition enclosing the condensation surfaces to a position designated bythe reference character 8 fully exposing the condensation surfaces tothe gas within the chamber I, or the hood can be positioned in anylocation intermediate the fully closed and fully opened positions inaccordance with the operating conditions of the pumping system.

The exterior surface of the hood 8 is covered with a thermal insulatingmaterial I4 which prevents the condensation surfaces from being exposedto any heat within the receiver during the time when the surfaces arebeing cooled to the operating temperature.

The servomotor for positioning the hood is controlled by a controldevice which is connected to a temperature sensor I located adjacent thecoil 4 for providing a continuous mea- I surement of the temperature ofthe condensation surfaces and thereby regulating the servomotor.

Before the pumping operation is commenced in the apparatus disclosed inFIG. I, the protective hood is closed separating the cooling coil 41from the remainder of the chamber I. The condensation surfaces providedby the coil d are reduced to a predetermined temperature and the chamberI is evacuated by a forepump I03 through a line 17 containing a valveIfI which is in the opened position. When starting vacuum for thepumping operation, for example mm. Hg and the predetermined temperatureof the condensation surfaces, for example, 20 Kelvin, have been reached,the protective hood 8 is opened and the pumping operation commencesunder full suction capacity. The establishment of the vacuum conditionswithin the receiver can be observed on the gauge l9 mounted on thereceiver.

FIGS. 2a and 2b, a receiver 21 provides a complete enclosure for achamber 22 arranged to contain a gas to be pumped under cryogenicconditions. In the lower portion of the chamber 22 a cooling coil 24forms the condensation surfaces for reducing the gas to the desired lowtemperature. An inlet line 25 and and outlet line 26 circulate arefrigerant through the cooling coil 24. A heat radiation shield 23surrounds the coil 24% and is formed along the sides and lower surfacesof the coiling coil 24 by a housing member 27 and the lower surface ofthis housing member is cooled by another cooling coil 28 soldered to itand through which another refrigerant flows at a higher temperature thanthat in the cooling coil 24 forming the condensation surfaces. The heatshield is completed by a radiation shield 29 which covers the uppersurface of the cooling coil. The radiation shield 29 is constructed of anumber of chevron-shaped sheets 30 arranged to prevent heat radiationwithin the receiver from being directed against the cooling coil 24.Encircling the angle sheets 31 is another cooling pipe 311 having aninlet line 32 and an outlet line 33 for flowing refrigerant through thepipe. The sheets 30 are supported by a frame 34 and, in turn, the frameis supported on a shaft 36 which extends through the wall of thereceiver at through a device effecting a vacuum seal. In addition, theinlet and outlet lines 32 and 33 for the cooling pipe 31 enter and leavethe chamber 22 through the shaft 36. The upper part 29 of the heatshield 23 enclosing the condensation surfaces can be pivoted by means ofa shaft 365 between a position, as shown in FIG. 2b, where it covers thecondensation surfaces to a position, shown in FIG. 2a, where the gaseswithin the receiver can flow over the condensation surfaces. Byselectively positioning the upper cover of the condensation surfaces theflow of gas over the cooling coil 2 3 can be regulated. The shaftsupporting the upper cover can be pivoted by hand or by a motor drive,such as shown in FIG. 2b comprising a gear transmission means 37 and aservomotor 38. A control device 39 is connected to the servomotor forpositioning the upper cover of the heat shield. The servomotor isconnected to a pressure gauge MI in such a manner, that after thepredetermined temperature, for example 20 Kelvin, has been reached thecondensation surfaces remain available for pumping as long as thepressure in the receiver does not exceed a predetermined value. Inaddition, a forepump II. is connected to the receiver through apreevacuation line 42 which contains a valve 33 for establishing thedesired vacuum conditions.

In FIGS. 3a and 3b, another embodiment of the present invention is shownproviding individual adjustment of the various elements forming the heatshield enclosure for the condensation surfaces which afford aparticularly advantageous gas throttling arrangement. A receiver 45encloses the space containing the gas to be pumped and, as with theother embodiments disclosed, the condensation surfaces are provided inthe lower region of the receiver by means of a cooling coil 46. Aplurality of vertically disposed heat protection sheets are providedwhich are rotatable about their vertical axes as indicated by FIG. 3b.The individual sheets 47 extend between an upper plate 38 and a lowerplate $9 and can be rotated jointly by means of a transmission devicecomposed of a central gear 50 and individual gears 51 each secured tothe upper end of one of the heat protection sheets 47. By means of thetransmission device the plates can be rotated selectively to anyposition between the fully opened and the fully closed positions. Foractuation of the transmission device, a vertically arranged shaft 53 issecured at its upper end to the driving gear 50 and extends downwardlythrough the cooling coil 46 and out of the receiver 45 through a packingdevice 52. Exteriorly of the receiver the shaft may be driven by hand orby means of a motor and gear transmission means as is shown in FIG. 3a.

Connected to the motor 54 is a control device 55 which is connected to apressure gauge 56 for measuring the pressure within the receiver and toa temperature sensor 57 positioned adjacent the cooling coil 46 fordetermining the temperature of the condensation surfaces. Duringoperation the condensa tion surfaces are completely enclosed by the heatprotection sheets d7 until the predetermined temperature, that is about20 Kelvin, is reached and then the gas inflow is regulated as a functionof the pressure within the receiver to maintain a certain pressure, thatis, about If) mm. Hg and the flow is throttled to a minimum. However,above this pressure the throttling is increased in an amount based onthe quantity of the condensing gas in accordance with the constantrefrigeration output. The constant refrigeration output depends on thecondensation temperature and the heat of condensation of the gas beingpumped. Accordingly, the gas inflow over the condensation surfaces mustbe adjusted so that at a given refrigeration output the correspondingquantity of gas is admitted to flow over the surfaces. The devicesdisclosed in FIGS. 2b and 3a employed, in accordance with the presentinvention, to insulate the condensation surfaces from the heat withinthe receiver at least during that part of the cooling of the surfaceswhen a predetermined temperature is being established, which temperaturecorresponds essentially to the operating temperature during pumping.Subsequently, by movably displacing the enclosure about the coolingcoil, the condensation surfaces are fully exposed to the heat within thereceiver. In accordance with this arrangement, it has been found that abetter utilization of the refrigerating apparatus is achieved in thatthe operating temperature and hence the full suction capacity of thepump, is reached in a much shorter time after commencing the coolingoperation than would be possible with the gas supply unthrottled and thecondensation surfaces unprotected from heat during the initial coolingperiod despite the unhindered gas inflow and therefore stronger pumpingduring that time.

In accordance with the general concept of the invention, the thermallyinsulating enclosure about the cooling coil can include any measureswhich effectively prevent the heat within the receiver from impinging onthe condensation surfaces. it can be appreciated, of course, that acomplete thermal insulation of the condensation surfaces is notpossible. However, to attain the object of the present invention, athermal insulation easily obtained by known measures, such as in tanksfor liquefied gas, is sufficient.

What we claim is:

1. A method of pumping a gas under cryogenic conditions comprising thesteps of providing an enclosed space for the gas to be pumped,positioning deep cooled condensation sur faces within the enclosedspace, thermally insulating the condensation surfaces from the heatsupply within the enclosed space while cooling the condensation surfacesto a predetermined low temperature and while colling the condensationsurfaces preventing the flow of the gas to be pumped over the surfaces,and regulating the flow of gas to the condensation surfaces after thepredetermined temperature is reached.

2. A method, as set forth in claim 1, wherein establishing vacuumconditions within the enclosed space for pumping the gas under cryogenicconditions.

3. A method, as set forth in claim 2, wherein cooling the condensationsurfaces to a temperature of about 20 Kelvin and regulating the gas flowover the condensation surfaces for maintaining the vacuum conditions atabout mm. Hg.

4. Apparatus for pumping gas under cryogenic conditions comprising wallsforming a closed chamber containing the gas to be pumped, means forforming condensation surfaces within the chamber for cooling the gas tothe requisite low temperature, means for enclosing said condensationsurfaces within said chamber for preventing the gas within said chamberfrom flowing over the condensation surfaces, means for thermallyinsulating said enclosing means for preventing heat within said chamberfrom affecting said condensation surfaces, and means for throttling theflow of gas within said chamber over said condensation surfaces.

5. Apparatus, as set forth in claim 4, wherein said enclosing means forsaid condensation surfaces comprising wall means surrounding saidcondensation surfaces and including a hood member, and said thermalinsulating means comprising thermal insulation material covering saidwall means including said hood for preventing heat from within saidchamber from contacting said condensation surfaces.

6. Apparatus, as set forth in claim 5, wherein said means for throttlingthe flow of gas comprising a shaft extending into said chamber and beingsecured to said hood, and means for engaging said shaft exteriorly ofsaid chamber for displacing said hood member from its position enclosingsaid condensation surfaces for variably admitting flow of gas to saidcondensation surfaces.

7. Apparatus, as set forth in claim 4, wherein said enclosing meanscomprising a housing enclosing a portion of said condensation surfaces,a cover for cooperation with said housing for completely enclosing saidcondensation surfaces, a cooling coil mounted on said housing forcirculating a cooling medium therethrough for removing heat from saidhousing and preventing the heat from reaching said condensationsurfaces, and said cover comprising a frame, a plurality of metallicplates mounted within said frame and arranged to prevent heat fromwithin said chamber from contacting said condensation surfaces, and asecond coil encircling said frame for removing heat therefrom.

8. Apparatus, as set forth in claim 7, wherein a rotatable shaftextending through said wall means into the interior of said chamber andbeing secured at its inner end to said cover, and means locatedexteriorly of said chamber for rotating said shaft and displacing saidcover from said housing and thereby admitting gas within said chamber toflow over said condensation surfaces within said housing].

9. Apparatus, as set forth in c arm 4, wherein said enclosing meanscomprising a pair of spaced plates located on opposite sides of saidcondensation surfaces, a plurality of rotatable plate sections extendingbetween said plates and being arranged in combination with said platesto completely enclose said condensation surfaces.

10. Apparatus, as set forth in claim 4, wherein said means forthrottling the flow of gas comprising a shaft member centrally locatedwithin said plate sections and extending into said chamber from theexterior of said wall means, a drive gear mounted on said shaft, aplurality of individual gears each mounted on one of said plate sectionsand in meshed engagement with said drive gear, and means for rotatingsaid shaft whereby said drive gear is rotated and in turn individuallyrotates said plate sections for selectively admitting gas for flow oversaid condensation surfaces.

11. Apparatus, as set forth in claim 4, wherein said condensationsurfaces comprising a cooling coil located within said chamber, andconduit means connected to said cooling coil for circulating arefrigerant therethrough.

12. Apparatus, as set forth in claim 4, wherein means being connected tosaid chamber for establishing a vacuum therein.

13. Apparatus, as set forth in claim 4, wherein a temperature sensorpositioned within said chamber adjacent said condensation surfaces, acontrol device operatively connected to said temperature sensor, anddrive means for opening and closing said throttle means being incommunication with said control device which regulates the extent of theopening of said throttle means by said drive means.

2. A method, as set forth in claim 1, wherein establishing vacuumconditions within the enclosed space for pumping the gas under cryogenicconditions.
 3. A method, as set forth in claim 2, wherein cooling thecondensation surfaces to a temperature of about 20* Kelvin andregulating the gas flow over the condensation surfaces for maintainingthe vacuum conditions at about 10 4 mm. Hg.
 4. Apparatus for pumping gasunder cryogenic conditions comprising walls forming a closed chambercontaining the gas to be pumped, means for forming condensation surfaceswithin the chamber for cooling the gas to the requisite low temperature,means for enclosing said condensation surfaces within said chamber forpreventing the gas within said chamber from flowing ovEr thecondensation surfaces, means for thermally insulating said enclosingmeans for preventing heat within said chamber from affecting saidcondensation surfaces, and means for throttling the flow of gas withinsaid chamber over said condensation surfaces.
 5. Apparatus, as set forthin claim 4, wherein said enclosing means for said condensation surfacescomprising wall means surrounding said condensation surfaces andincluding a hood member, and said thermal insulating means comprisingthermal insulation material covering said wall means including said hoodfor preventing heat from within said chamber from contacting saidcondensation surfaces.
 6. Apparatus, as set forth in claim 5, whereinsaid means for throttling the flow of gas comprising a shaft extendinginto said chamber and being secured to said hood, and means for engagingsaid shaft exteriorly of said chamber for displacing said hood memberfrom its position enclosing said condensation surfaces for variablyadmitting flow of gas to said condensation surfaces.
 7. Apparatus, asset forth in claim 4, wherein said enclosing means comprising a housingenclosing a portion of said condensation surfaces, a cover forcooperation with said housing for completely enclosing said condensationsurfaces, a cooling coil mounted on said housing for circulating acooling medium therethrough for removing heat from said housing andpreventing the heat from reaching said condensation surfaces, and saidcover comprising a frame, a plurality of metallic plates mounted withinsaid frame and arranged to prevent heat from within said chamber fromcontacting said condensation surfaces, and a second coil encircling saidframe for removing heat therefrom.
 8. Apparatus, as set forth in claim7, wherein a rotatable shaft extending through said wall means into theinterior of said chamber and being secured at its inner end to saidcover, and means located exteriorly of said chamber for rotating saidshaft and displacing said cover from said housing and thereby admittinggas within said chamber to flow over said condensation surfaces withinsaid housing.
 9. Apparatus, as set forth in claim 4, wherein saidenclosing means comprising a pair of spaced plates located on oppositesides of said condensation surfaces, a plurality of rotatable platesections extending between said plates and being arranged in combinationwith said plates to completely enclose said condensation surfaces. 10.Apparatus, as set forth in claim 4, wherein said means for throttlingthe flow of gas comprising a shaft member centrally located within saidplate sections and extending into said chamber from the exterior of saidwall means, a drive gear mounted on said shaft, a plurality ofindividual gears each mounted on one of said plate sections and inmeshed engagement with said drive gear, and means for rotating saidshaft whereby said drive gear is rotated and in turn individuallyrotates said plate sections for selectively admitting gas for flow oversaid condensation surfaces.
 11. Apparatus, as set forth in claim 4,wherein said condensation surfaces comprising a cooling coil locatedwithin said chamber, and conduit means connected to said cooling coilfor circulating a refrigerant therethrough.
 12. Apparatus, as set forthin claim 4, wherein means being connected to said chamber forestablishing a vacuum therein.
 13. Apparatus, as set forth in claim 4,wherein a temperature sensor positioned within said chamber adjacentsaid condensation surfaces, a control device operatively connected tosaid temperature sensor, and drive means for opening and closing saidthrottle means being in communication with said control device whichregulates the extent of the opening of said throttle means by said drivemeans.